The developing activity of 1-ascorbic acid (vitamine C) and some chemical analogues is known since many years in the photographic art. In their report on the synthesis of iso-ascorbic acid (iso-vitamine C or d-arabo-ascorbic acid) in Berichte, Vol.67, p. 1239 (1934) Maurer at al. for the first time report tests on ascorbic acid and its optical isomer as developers for a photographic plate and describe them as active developers superior to conventional aromatic developers. However in most later studies ascorbic acid and derivatives are regarded as rather weak developers by themselves. So there are several publications on developers containing a superadditive combination of a conventional developing agent and an ascorbic acid derivative used as auxiliary developer or as an antioxidant. U.S. Pat. No. 2,688,549 discloses the combination of a 3-pyrazolidone developing agent and of an ascorbic acid derivative. GB 1 266 533 describes the combination of a p-hydroxybenzene developing agent, an ascorbic acid and sulphite ions. An equally good developing activity for both surface and internal latent images is claimed in U.S. Pat. No. 3,826,654 which discloses a combination of a 3 -pyrazolidone an ascorbic acid, a heterocyclic thione or thiol and an alkali iodide at a pH of at least 12. The concentration of the ascorbic acid ranged from 0.05 moles to 0.4 moles per liter. The most preferred pH range was 13 to 14.
Several compositions specifically for high contrast development are published. So U.S. Pat. No. 3,942,985 discloses the combination of an iron chelate developer and an ascorbic acid. U.S. Pat. No. 4,756,997 claims a combination of a p-hydroxybenzene, an auxiliary developer an antifoggant, an antioxidant and an -ketocarboxylic acid wherein the antioxidant can be ascorbic acid.
An application wherein ascorbic acid is the principal developing agent is disclosed in the Japanese Unexamined Patent Publication (Kokai) 59-191035 the reduction or omission of the washing step in the processing cycle is claimed as unexpected advantage. The concentration of ascorbic acid ranges from 0.2 to 20 g/l in case of immersion processing and from 0.5 to 1OO g/l in case of coating development. A pH of 10 to 12 is preferred for immersion processing and of 11 to 14 for coating types of development.
Chemical analogues of ascorbic acid that show developing activity too include (iso)ascorbic acid ketals or acetals as disclosed in GB 1 142 135, dihydroxyfuran derivatives as described in J. Phot. Sci., Vol. 19 (1971), p. 211, and imino-ascorbic acid derivatives as claimed in U.S. Pat. No. 2,688,548.
A first study on the kinetics of development by ascorbic acid by T. H. James was published in J. Am. Chem. Soc. Vol. 66 (1), p. 91 (1944). The results of a more extensive study by Willis and Pontius appeared in Phot. Sci. Eng. Vol. 14 (6), p. 384 (1970). The autors concluded to a two step mechanism including an induction period and a continuation step with different activation energies.
In graphic and reprographic arts the accurate sharp reproduction of line edge and screen dot originals is of uttermost importance. This goal is reached by the combination of specially designed graphic arts materials and appropriate processing systems producing so-called "lith quality". A first group of such processing systems consists of the traditional "lith developers" characterized by the presence of hydroquinone as the sole developing agent and a low sulphite ions content giving rise to an infectious development mechanism. However these conventional developers are rather instable in time and require complicated regeneration systems for both oxidation and exhaustion. In more recent times so-called "hard dot Rapid Access" developers were introduced on the market which combine a good stability with a "lith quality" in the reproduction of edges and screen dots. Examples of such developers and corresponding appropriate photographic materials include the GRANDEX system, marketed by FUJI PHOTO Ltd. AGFASTAR, marketed by AGFA-GEVAERT N.V. and the ULTRATEC system, marketed by EASTMAN KODAK Co. However all these developer systems show some disadvantages from an ecological or toxicological point of view. E.g. hydroquinone is a rather unwanted ingredient because of its allergenic effects. The biodegradation of disposed Phenidone is too slow. Sulphite ions show a high COD (Chemical Oxygen Demand) and the resulting sulphate ions are harmful for e.g. concrete. As a consequence it is undesirable that depleted solutions of this kind would be discharged into the public sewerage; they have to be collected and destroyed by combustion, a cumbersome and expensive process. As a consequence residual solutions containing sulphite produce emissions containing sulphurdioxide and/or sulphurtrioxide on combustion. On the other hand, some "hard dot Rapid Access" systems are ecologically suspect due to the presence of hydrazine or hydrazide derivatives and/or the presence of amino compounds which can be toxic or too volatile as stated in U.S. Pat. No. 4,975,354. It is possible that unwanted organic solvents are used in order to introduce some water insoluble compounds into the photographic material. Some of these suspect compounds can be washed out partially on development. So there is a permanent need for developing solutions which can be disposed of in a safer way for the environment and which are more consumer-friendly.
In a few cases ascorbic acid is described as showing some activity as a "lith developer". In his study on the mechanism of lith development, published in J. Phot. Sci. Vol. 27 (1979), p. 185, Zwicky shows that a lith effect can occur with ascorbic acid as the sole developing agent and he illustrates the effect with photographs showing reproduced line edges and contact screen dots. The developing solution employed contained 112 g of ascorbic acid per liter, potassium bromide, formaldehyde bisulphite and sodium hydroxide to establish a pH of 10.5. However even with this high concentration of ascorbic acid the rate of formation of developed silver was considerably slower compared to a conventional hydroquinone lith developer. As a result the slope of the characteristic or sensitometric curve was appreciably lower than with hydroquinone. Eventually no commercially usable developer resulted from Zwicky's formula.
In Miller U.S. Pat. No. 3,386,824 a processing solution of high pH containing a high concentration of iso-ascorbic acid is disclosed. However this solution is embedded in plastic micro-capsules and not intended for conventional immersion processing.
It is an object of the present invention to provide a processing solution which can be treated after use in a safe way for the environment and which use is more consumer-friendly.
It is a further object of the present invention to provide a processing solution of a simple composition for immersion processing and easy to replenish that produces hard dot quality as an alternative to existing lith developers and hard dot Rapid Access developers.
Further objects will become apparent from the description hereafter.